Method for charging and discharging lithium secondary battery, and system for charging and discharging lithium secondary battery

Abstract

A charge/discharge method for a lithium secondary battery is performed on a lithium secondary battery including a positive electrode containing a positive electrode active material capable of occluding/releasing lithium ions; a negative electrode containing a negative electrode active material capable of occluding/releasing lithium ions; a separator located between the positive electrode and the negative electrode; and an electrolyte having a lithium ion conductivity. The positive electrode active material contains a lithium-containing transition metal oxide; and a reversible capacity of the negative electrode is larger than a usable capacity of the positive electrode. First charge/discharge is performed by which the positive electrode in a charged state is discharged until having a first potential VDp1, which is lower than 2.7 V on a lithium metal basis, and the discharge is finished at this point.

Description

TECHNICAL FIELD[0001]The present invention relates to a charge / discharge method and a charge / discharge system for a lithium secondary battery.BACKGROUND ART[0002]Lithium secondary batteries have a large capacity and a high energy density and are easy to be decreased in size and weight, and therefore are widely used as power supplies of small-sized mobile electronic devices, for example, mobile phones, personal digital assistants (PDAs), laptop personal computers, camcorders, portable game machines and the like. In the future, such small-sized mobile electronic devices are desired to have a larger number of functions and to be drivable for a longer time.[0003]In order to attain a further increase in the capacity of lithium secondary batteries, development of active materials is under way. As positive electrode active materials, lithium-containing transition metal oxides, for example, are used. Known lithium-containing transition metal oxides include lithium-containing complex oxides ...

AI Technical Summary

Benefits of technology

[0014]According to the present invention, in a charge / discharge method for a lithium secondary battery in which a lithium-containing transition metal oxide is used as a positive electrode active material and an irreversible capacity of a negative electrode is larger than a usable capacity of a positive electrode, the discharge end potential of the positive electrode is set to a potential lower than 2.7 V. According to the charge / discharge method of the present invention, the deterioration specific to the lithium-containing transition metal oxide caused by the repetition of the charge / discharge cycles can be utilized to gradually decrease the negative electrode utilization factor as the charge / discharge cycle repetition proceeds. As a result, the deterioration of the negative electrode (deposition of lithium), which would be otherwise caused by the repetition of the charge / discharge cycles, can be prevented without decreasing the initial battery capacity. Accordingly, the initial battery capacity can be kept high, and the decrease in the battery capacity caused especially by the long-term repetition of the charge / discharge cycles can be suppressed.

Problems solved by technology

However, there is a problem that a lithium secondary battery using LiNiO2 has a short charge / discharge cycle life due to the low stability of the crystalline structure of LiNiO2.

These materials occlude / release a large amount of lithium.

When this occurs, electron conductivity is not provided, which may undesirably decrease the capacity and also cause lithium metal to be deposited on the current collector.

However, when the amount of lithium to be occluded / released to / from the positive electrode active material is decreased, neither the capacity nor the long-term cycle life can be improved although a certain effect of improving the reversibility is provided.

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